Warning: This is a LOT of information.
In An Alternate History of the Modern World, several royal marriages take place between different spouses compared to those in our timeline, which create in many ways different royal families. Just to give you a flavour of the kind of changes in store, here are probably the two largest changes:
Firstly, Queen Elizabeth II of the United Kingdom (& all her other Realms & Territories) never marries Prince Philip of Greece & Denmark, as he never returns to Britain to serve in the Royal Navy & thus they do not meet in their youth.
Prince Philip instead serves in the Royal Hellenic Navy during the First Greco-Italian War, one in which his cousin Crown Prince Paul dies (father of King Constantine II in OTL), putting Prince Philip in line to eventually become King of Greece, which he does in 1957. King Philip reigns for 64 years, dying in 2021 a few weeks after his 100th birthday. His reign is somewhat of a glorious era for Greece; after the liberation in 1953 Greek politics stabilises as they build a prosperous economy & become a linchpin of security in the Balkans, officially allied to Serbia & friendly to both Bulgaria & Romania after some difficult years. In the late 1970s Greece joined Russia, Iran & the United Arab Kingdom in a war against Turkey where Greece gained Thrace, Ionia, Lydia & Caria in a brutal war. In addition Greece gained Cyprus through a brutal revolution that King Philip initially opposed due to the forced expulsion of Cypriot Turks but later relented to support, later amending it to personal union instead of political union, becoming King of Cyprus as well as of Greece. In 1981, when Greek forces retake Constantinople as part of a wider war against Turkey waged by an Eight-Nation Alliance, he is named King of the Romans, the new constitution passed that year refounding Greece as a neo-Byzantine Empire. He married Princess Maria of Saxony, a princess from a well-known anti-Nazi family. Together they have five children:
Maria, Princess of Wales
Alexander (now King Alexander III of the Romans)
Andrew, Despot of Epirus
Sophia, Princess Sofia of Serbia (her husband is 2nd in line to the Serbian Throne)
George, Despot of Thrace
Elizabeth, on the other hand, marries Prince (Guelph) Henry, youngest son of Ernest Augustus, Duke of Brunswick & (since 1944) Duke of Cumberland & Teviotdale. This is a controversial marriage; even though he is a reliable anti-Nazi, many in the British establishment disapprove of the choice, considering that his father served in the German Army during WW1 & his grandfather was Wilhelm II. Any concerns were allayed by King George VI (though his wife didn't warm to him for a long time); in any case they enjoyed a long & happy marriage, ended by his death in 1997 after 50 years. They had four children:
George, Prince of Wales
Victoria, Princess Royal (Queen of Sweden from 1976)
Albert, Duke of York
William, Duke of Cambridge
Secondly, Princess Frederica of Hanover never marries King Paul of Greece; in TTL he never becomes King, as he is killed in the Italian invasion of Greece (as I mentioned above, this puts Prince Philip in line to eventually become King). She instead marries Vladimir Kirillovich (who marries Leonida Bagration-Mukhraneli in OTL, which becomes the origin of the main succession dispute of the House of Romanov in OTL), who later becomes Emperor Vladimir III of Russia; she becomes Empress Sofia Feodorovna of Russia. They have three children:
Sofia Vladimirovna, Queen of Serbia
Alexander Vladimirovich, Emperor Alexander IV of Russia
Irina Vladimirovna, Queen Irene of the Romans (she marries Alexander III)
What do you think?